Katabolism

Katabolism, or destructive metabolism, is a term employed in physiology, especially in that of plants, for all the processes of decomposition by which the relatively complex organic substances in the living organism are spontaneously broken down into relatively simpler substances. These processes are largely produced by zymoses or unorganised ferments (q.v.), such as diastase (q.v.), invertin, emulsin, and peptogenes; but simple oxidation also occurs. Respiration (q.v.) is to a great extent a conditioning cause, and in part a result, of katabolism. The products of the process are those waste-products, such as carbon-dioxide and water, which are exhaled, the organic acids, aromatic substances, colouring-matters, glucosides, alkaloids and waxes, which may be excreted by glandular action or may only be secreted; and also some of the plastic materials. Growth and movement involve a dissipation of energy, requiring a supply of oxygen and resulting in the giving-off of heat and even in some cases of light. [Phosphorescence.] The heat evolved is generally not sufficient to produce a sensible rise of temperature, but it does so in germinating seeds, as in malting, and in some cases of flowering, such as that of the aroids. [Physiology.]